1. Field of the Invention
The present invention relates to internal combustion engines and, more particularly, to a inner piston disposed inside a bore within an outer piston, the inner piston being coupled to the connecting rod in the usual manner, and the outer piston being coupled to a carrier which is slidably mounted in the slot of a forked lateral projection at the upper end of the connecting rod.
2. Description of Related Art
The reciprocating components of most piston driven engines include, essentially, one or more of a crankshaft, a connecting rod, a wrist pin and a piston. Internal combustion engines are known to achieve higher efficiency and performance with a high compression ratio. High compression engines do have a disadvantage, however. When operated at o.t. or w.o.t, the high pressure created within the combustion chamber of the cylinder after ignition tends to cause a secondary post-ignition explosion. This condition is commonly known as engine "knock". On the other hand, low compression engines suffer far less from knock at open throttle. When throttled, however, low compression engines are less efficient than high compression engines and tend to achieve less complete combustion of fuel. It is therefore desirable to have an engine with a variable compression ratio in order to receive the benefits of both a high compression ratio and a low compression ratio.
U.S. Pat. No. 4,137,873, issued to Caswell, Sr., on Feb. 6, 1979, shows a piston providing a flexible top wall adjacent the combustion chamber which allows the head of the piston to compress downwardly toward the base of the piston in response to pressure within the combustion chamber.
U.S. Pat. No. 4,203,406, issued to Smith on May 20, 1980, shows a piston which is in two pieces, a piston skirt integral with and depending from the piston head, and a sleeve cooperating with the piston skirt. The skirt and sleeve are in a telescoping relationship and are kinematically linked to each other and to the crankshaft of the engine. The connecting rod is pivotally attached to the sleeve by a wrist pin. The connecting rod extends into the piston head and is pivotally attached to a secondary connecting rod by a second wrist pin which is in turn pivotally attached the piston skirt by a third wrist pin. In this manner, the piston head is raised to a maximum elevation at both the end of the compression stroke and the end of the expansion stroke. The piston head and skirt are lowered to a lower elevation relative to the sleeve during the balance of the work stroke.
Pistons having a variable compression ratio can also be beneficial by increasing the fuel efficiency of two-stroke engines, four-stoke cycle engines and improving the cold-start and warm-up behavior of these engines. Pistons have been designed to realize the aforementioned benefits, and are made up of an outer piston part and an inner piston part, which is pivotally attached to the connecting rod. These pistons use hydraulic fluid which is forced in and out of the space between the two piston parts to raise and lower the compression ratio within the combustion chamber.
The following teach examples of pistons having variable compression height which use hydraulic forces to raise and lower the compression ratio: U.S. Pat. No. 3,200,798, issued to Mansfield on Aug. 17, 1965, which adapts the variable piston for two-cycle engines; U.S. Pat. No. 4,979,427, issued to Pfeffer et al., on Dec. 25, 1990, which adds temperature sensitive variation of the piston; and U.S. Pat. No. 5,247,911, issued to Nenicka et al., on Sep. 28, 1993, which adds a compression ratio control system that is external to the variable piston.
Two part pistons perform functions other than the variation of the compression ratio. U.S. Pat. No. 1,905,062, issued to Schaeffers on Apr. 25, 1933, shows a two part piston having a secondary piston linked to the connecting rod. The secondary piston controls air intake in a two-stroke cycle engine thereby improving efficiency and performance.
Another performance deficiency that can be improved by using a two part piston arises during the initial portion of the combustion cycle, the power stroke, of an internal combustion engine. The relationship between the piston, connecting rod, and crankshaft at TDC (top-dead-center) does not permit the transfer of lateral forces acting on the top of the piston into torque for rotating the crankshaft. U.S. Pat. No. 2,368,412, issued to Cords on Jan. 30, 1945, shows a piston which is provided with two relatively movable parts, one part being pivoted relative to the other part, provided with a crank arm connection between this pivoted portion and the connecting rod. Four wrist pins are required to complete the linkage between the two relatively moveable parts, the link, the crank arm, and the connecting rod. During an explosion at TDC, torque for rotating the crankshaft is applied by the pivoted portion via a link to the crank arm and connecting rod. U.S. Pat. No. 4,463,710, issued to McWhorter on Aug. 7, 1984, shows another two part piston designed to apply torque for rotating the crankshaft at TDC. The connecting rod is pivotally linked to a piston slider by a wrist pin, which is slidably mounted in the internal volume of the piston head. The piston head is pivotally mounted to a carrier by a second wrist pin, which is in turn slidably mounted in an inclined slot in the connecting rod. Changes in the angularity of the connecting rod, caused by rotation of the crankshaft, result in the piston being alternately raised and lowered as the carrier slides to the right and to the left of the inclined slot.
German Patent Application Number 3,222,568, dated Dec. 22, 1983 shows a double piston assembly wherein the main piston has an inclined cylinder in top as a combustion chamber containing a small piston. The small piston is pivotally attached to a linking member by a wrist pin. The linking member is pivotally attached by a second wrist pin to a lateral projection of the connecting rod. The main piston is attached to the connecting rod by a third wrist pin in the usual manner. The design of the small piston is such that it applies torque for rotating the crankshaft when acted on at TDC.
None of the prior art variable compression two part pistons utilize the larger of the two parts to apply torque to the crankshaft at top dead center via a forked lateral projection of the connecting rod. Nor are any of the prior art pistons attached to the connecting rod via a sliding carrier member within which the wrist pin is pivotally carried. Nor do any of the prior art two part pistons have the piston wrist pins attached to the connecting rod with an offset such that both pistons do not simultaneously achieve a TDC relationship with respect to the connecting rod and crankshaft.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.